Unordered: Fix unnecessary_copy_tests + extra tests.

It looks the odd result in unnecessary_copy_tests on Visual C++ 11 is not a
bug, but add some extra tests just to make sure. Also some extra rehash and
reserve testing thrown in.

[SVN r80705]

test/unordered/unnecessary_copy_tests.cpp

@@ -374,7 +374,16 @@ namespace unnecessary_copy_tests
         // COPY_COUNT(1) would be okay here.
         reset();
         x.emplace();
+#   if BOOST_WORKAROUND(BOOST_MSVC, >= 1800)
+        // This is a little odd, Visual C++ 11 seems to move the pair, which
+        // results in one copy (for the const key) and one move (for the
+        // non-const mapped value). Since 'emplace(boost::move(a))' (see below)
+        // has the normal result, it must be some odd consequence of how
+        // Visual C++ 11 handles calling move for default arguments.
+        COPY_COUNT(3); MOVE_COUNT(1);
+#   else
         COPY_COUNT(2); MOVE_COUNT(0);
+#   endif
 #endif
 
         reset();